May 23, 2012 —

Science Daily/Northwestern University

 A new Northwestern University study shows that the biological clock is not the only clock women trying to conceive should consider. The circadian clock needs attention, too.

"If you disrupt your internal rhythms, there will be negative consequences -- that is very clear," said Keith Summa, first author of the paper and an M.D./Ph.D. candidate working in Turek's lab. "Our results suggest people should consider their biological rhythms for optimal health."

The repeated shifting of the light-dark cycle shifts the biological clock throughout the body. This environmental disturbance is more relevant to shift workers and those frequently flying across time zones, the researchers note, than genetic disruption of the circadian clock, which also negatively influences reproductive function.

Epidemiological studies have shown female shift workers, such as nurses, and female flight attendants who work on long-distance east-west routes (i.e., those with constant jet lag) have fertility and menstrual issues. They are habitually out of sync with the external light cycle. But the role circadian rhythm disruption may play in their reproductive problems is a poorly studied area.

"We were surprised at how dramatic the effect of manipulating the light-dark cycle was, especially in the phase-advanced group," Summa said. "We expected a negative effect from the circadian clock disruption, but not this much."

"Our results have important implications for the reproductive health of female shift workers, women with circadian rhythm sleep disorders and/or women with disturbed circadian rhythms for other reasons,"

http://www.sciencedaily.com/releases/2012/05/120523200754.htm